1. Field of the Invention
The present invention pertains to safety needle instruments and, more particularly, to safety needle instruments including needles having sharp tips for penetrating anatomical tissue and safety members spring biased to an extended, protruding position to prevent inadvertent contact with tissue by the sharp needle tips.
2. Discussion of the Prior Art
Safety needle instruments have been proposed to gain access to anatomical cavities for many various procedures. Proposed safety needle instruments typically include a needle having a sharp tip for penetrating anatomical tissue and a safety member biased to move to an extended, protruding position to cover the sharp tip of the needle once the needle has entered the anatomical cavity. Accordingly, the safety member protects tissue and organ structures within the anatomical cavity from accidental injury by contact with the sharp tip of the needle after penetration or puncture of a wall of the anatomical cavity.
When the penetrating procedure is commenced, the distal end of the safety needle instrument is placed in contact with the anatomical cavity wall; and, as force is exerted on the safety needle instrument, contact of the safety member with the cavity wall moves the safety member proximally to a retracted position against the spring bias to expose the sharp tip of the needle to permit the sharp tip to penetrate the cavity wall. Accordingly, the force required to penetrate the cavity wall includes not only the force required to pass the safety needle instrument through the anatomical cavity wall but also the force required to overcome the spring bias on the safety member. Once the sharp tip of the needle has entered the anatomical cavity, the spring bias on the safety member overcomes the reduced proximal force on the safety member causing the safety member to move distally to the extended, protruding position. In practice, however, a residual proximal force is still applied to the safety member after penetration of the sharp needle tip into the cavity due to contact with surrounding tissue and/or tissue trapped between the safety member and the cannula and/or the needle, and the residual force is capable of preventing distal movement of the safety member to the extended, protruding position. To assure distal movement of the safety member upon entry of the safety needle instrument into the anatomical cavity, the strength of the spring biasing the safety member distally can be increased; however, increasing the strength of the bias spring also increases the force required to penetrate the cavity wall which is undesirable. Accordingly, currently available safety needle instruments with safety members utilize bias springs of strengths compromising force-to-penetrate and assured safety member distal movement in an attempt to satisfy both requirements.